The present invention relates to apparatus for gas carburizing the bore in objects used in mechanical engineering and metallurgy. It may be implemented with utmost effectiveness in strengthening the bore of pipes handling abrasive materials, e.g., pulp, or used for the pneumatic conveying of bulk materials.
Disclosed in USSR Inventor's Certificate No. 492,569 is an apparatus for the thermal strengthening of pipes consisting of a heating device and a sprayer for cooling which are both accommodated in a common nozzle along with concentrically arranged tubes for feeding a gas-air mixture and water. Designed for hardening the bore of pipes, this apparatus is of comparatively simple construction, its main elements being a heater in the form of a gas burner and a sprayer. Yet, this apparatus is unsuitable for the treatment of bores by the gas carburizing technique since it lacks means of sealing off the bore of the treated object at the end faces. Moreover, the known apparatus is not provided with a system for the automatic feeding of carburizing gas into said bore of the treated object.
Also known is an apparatus for the electric resistance heating of hollow objects disclosed in USSR Inventor's Certificate No. 283,269 comprising contact clamps applied to the end of the object, an evacuation system with a sealing arrangement in the form of cones displaced by means of a drive, and hollow mandrels connected to the evacuation system. Designed to produce a bright finish of the pipe bore in the course of resistance annealing of pipes, this apparatus incorporates, as indicated above, sealing cones with a drive imparting motion thereto, current-feeding contact clamps and hollow mandrels connected to the evacuation system so as to evacuate air from the bore of the treated pipe. However, as far as gas carburizing of bores is concerned, this apparatus is of no avail because uniform heating of the pipe walls is hardly achievable with the resistance heating technique and, as a consequence, the process of carburizing goes on at a rate which is anything but uniform. The carburized case so formed is of varying depth, impairing the quality of the product. Another point is that the lack of a support along the length of the pipe brings about residual deformation manifesting itself in the bending of pipes.
With the hydraulic and pneumatic conveying of abrasive materials by pipelines coming into vogue, there is an everincreasing demand for pipes with high-strength bores. All the known apparatus fail to meet this demand and, as a result, difficulties are experienced in operating pipelines for the pneumatic or hydraulic conveying of pulp and other abrasive materials.